It's a dilemma extremely familiar to anyone with social anxiety –
for how long to make eye contact before looking away?

The fear is that if you only ever fix the other person's
gaze for very brief spells then you'll look shifty. If you lock
on for too long, on the other hand, then there's the risk of
seeming creepy. Thankfully a team of British researchers has now
conducted the most comprehensive study of what people generally
regard as a comfortable length of eye contact.

The participants' main task was to sit close to a monitor
and watch a series of video clips of the same actor or actress
making eye contact with them for various durations between 100ms
(a tenth of a second) and 10,300ms (just over ten
seconds).

The participants' pupil dilation was recorded while they
watched the brief clips, and after each clip they had to say
whether the length of eye contact felt too long or too short for
comfort. Each participant watched 40 clips of the same actor or
actress, but there were 8 actors and actresses used in the study,
all of them Caucasian. The participants also filled out a
personality questionnaire and they rated the actor or actress
who'd appeared in their clips for various characteristics
including attractiveness and threat.

On average, the participants were most comfortable with eye
contact that lasted just over three seconds. Looking at the
distribution of preferences, the vast majority of participants
preferred a duration between two and five seconds. No-one
preferred eye contact durations of less than a second or longer
than nine seconds.

Surprisingly, there were no links between the participants'
personality profiles and their preferences for length of eye
contact. There were also no major effects of participant age or
gender – the only exception being that among male participants
looking at clips featuring an actress, the older the man, the
more likely he was to prefer longer eye contact. In terms of the
participant ratings of the actor or actress, only threat was
relevant, with participants who rated their actor or actress as
more threatening tending to prefer shorter eye contact
durations.

The researchers were interested in the participants' pupil
dilation because it's a marker of physiological arousal. They
found that participants who showed greater pupil dilation in
response to the video clips tended to prefer longer eye contact.
The meaning of this finding is unclear – negative emotions
usually elicit more arousal, so we might have expected the
opposite result.

The researchers speculated that the greater physiological
arousal in this context might be traceable to a rapid, automatic
form of face processing that takes place in subcortical areas of
the brain, and that "activity within this early eye contact
processing stage is enhanced in participants who favour longer
periods of direct gaze and who presumably feel more comfortable
in engaging in a communicative link."

A major issue with the study is of course that it used
pre-recorded video clips rather than a live interaction. Readers
will rightly wonder just how fair it is to extrapolate from this
setup to the real life situation of two people in conversation,
where both parties are involved in the dance of eye
contact.

In fact, the lack of realism in the study may explain why
no association was found between personality and preferred gaze
duration. However, the researchers point out that their finding
of an average preferred eye contact length of 3.3 seconds tallies
with some preliminary studies published in the 1970s that did
involve participants interacting in pairs.